Parental origin of the extra chromosome in trisomy 18

The parental origin of the supernumerary chromosome 18 was investigated by RFLP analysis in 23 individuals with Edwards syndrome. All families were studied with the DNA probe pERT-25, which recognizes a locus of highly polymorphic tandemly repeated DNA sequences on chromosome 18. The extra chromosome was found to be of maternal origin in 19 patients (95%), of paternal origin in one patient (5%), and indeterminate in three patients. In one of the three indeterminate cases, a mosaic, an apparent recombination event had taken place within the pERT-25 locus. The overall high degree of informativeness of pERT-25 illustrates the power of a chromosome-specific variable-number tandem repeat probe (VNTR) in parental origin studies of aneuploidy.